1. Field of Invention
The present invention relates to a positioning method and system, and more particularly to a positioning method and system that utilize the transmission time from the base stations in two or more cellular networks to the targeted mobile respectively to estimate the position of the mobile phone.
2. Description of Related Arts
With the development of the mobile communication technique, especially after US demands for emergency location services, positioning services are getting more and more attention in the industry.
Depending on whether active participation of mobile phone is required or not, the positioning technique in cellular communication systems is classified into two categories: positioning technique requiring information submission from the targeted mobile phone and positioning technique requiring no information submission from the targeted mobile phone.
As to the former technique, the positioned statement of the targeted mobile phone can be determined by sending control signaling to the mobile phone and receiving relevant measurement reports actively reported by the mobile phone. So the mobile phone can figure out when it is being positioned. And the mobile phone can prevent from being positioned by not reporting relevant measurements or reporting false information, so as to protect its position information.
However, as to the latter technique that requires no active participation of mobile phone, the mobile phone cannot determine whether it is being positioned or not, which causes difficulty to protect the position information. A typical technique of this category is the positioning method based on cell ID.
According to the reference signals, the positioning technique is mainly classified into three categories: the positioning technique based on severing cell ID for the targeted mobile phone, the positioning technique based on the base station(s) and the targeted mobile phone signals, and the positioning technique based on the satellite navigation system(s). The positioning technique based on cell ID for the targeted mobile phone has poor accuracy; the positioning technique based on satellite navigation system(s) requires extra components and cost, and the positioning technique based on the base station and the targeted mobile phone signals basically do not require extra components with moderate accuracy.
The traditional positioning technique based on the base station and mobile phone signal transmission time, such as U.S. Pat. No. 5,600,706, is illustrated in FIG. 1. The positioning system requires at least three base stations 111-113 and a mobile phone with measurement function 12. The transmission time of the wireless signal between the base station 111-113 and mobile phone 12 is t1, t2 and t3 respectively. As the velocity of radio waves is equal to the speed of light (c), the distance between the mobile phone and the respective base station is di=ti*c (i=1, 2 . . . ). Draw circles 141-143 with the respective base station as center and di as radius, and the intersection point of the circles is where the targeted mobile phone is. The mobile phone measures the transmitting-receiving time delay of the base station and reports it to the network, and the network can calculate the location of the mobile phone based on the measurement data.
Due to the obstruction such as building block between the mobile phone and the base station, the sight of light rarely exists in the real network. As shown in FIG. 2, a building 23 stands between the base station 21 and the mobile phone 22, so there is no LOS (Light Of Sight) 24 between them. At the same time, another building 25 reflects the base station signal to the mobile phone 22, so there is a signal transmission path 26 between the base station and the mobile phone. According to the principle of the total length with two sides being greater than the third in any triangle, the calculated value of radius is greater than the real value, which causes the inaccuracy in determining the mobile phone location. At present, a few processing methods based on indirect path detection and positioning system with indirect path have been developed.
The 3G (3rd Generation) mobile communication system is being applied or will be applied in the most countries and regions in the world. The 3GPP (3rd Generation Partnership Project), as the 3G standards organization, has completed all works on standards. In the positioning aspect in the cellular communication systems, taking suggestions from all companies, the 3GPP adopts all of the three positioning methods: the positioning technique based on cell ID of the serving base station, the positioning technique based on the base station and mobile phone signal transmission time, and the positioning technique based on the satellite navigation system(s).
The measured data submission is requested in the positioning technique based on the base station and the mobile phone signals. The mobile phone measures the signal transmission time between the mobile phone and the base stations and reports it to the network via signaling, and the network estimates the position of the mobile phone.
According to the conclusion of many references, the more base stations that the mobile phone measures, the more accuracy the result is. However, in a real network, due to the cost of the base station and the difficulty for the network planning, the number of the base stations with one certain mobile phone to measure in a real network is limited. As dual-mode or multi-mode mobile phone can receive signals from base stations in different networks, the mobile phone can be positioned in each network. However, it is hard to tell which result is more accurate.